The present invention relates to an image forming apparatus for successively feeding sheet-like objects by means of an automatic document feeder and copying the image information regarding images formed on the objects.
A copying apparatus that utilizes an electrostatic copying process is an example of an image forming apparatus. In the copying apparatus, an image on a document to be copied is represented in the form of image information that indicate the light and shade portions of the image. An electrostatic latent image is formed on a photosensitive body in accordance with the image information, and the electrostatic latent image is then visualized with toner (i.e., a developer), thus making a copy of the document.
A developer image, i.e., the visualized latent image, is output to recording mediums, such as sheets of paper.
An automatic document feeder, which successively feeds sheet-like objects to an image formation section one by one, is in widespread use since the use of such a feeder helps lighten the load that is imposed on the user at the time of a copying operation.
In the case where copies are made, with original documents being successively fed by an automatic document feeder, a document feed error (a paper jam or a document jam) may occur in the feeding mechanism of the automatic document feeder. In this happens, several of the original documents, which are being fed then, will stop and stay at different positions inside the automatic document feeder.
If, due to the document jam, a number of original documents stay at different positions inside the document feeder, the user has to determine which document should be returned to the automatic document feeder. To be more specific, the user has to compare the images on the copies discharged and stacked on a discharge section of the copying apparatus with those images which are shown on the documents which are being fed or have not yet been fed at the time of the document jam. By this comparison, the user discriminates between documents from which image information have already been copied and documents from which image information have not yet been copied. After re-setting the documents that have to be returned to the automatic document feeder, the copying operation is resumed.
If the original documents are sheets which bears images on both sides, or if the copies produced by the copying operation are sheets which bear images on both sides, the operation for identifying documents that should be returned to the automatic document feeder, requires much time, and the time needed for the copying operation is inevitably long.
It is likely that the documents from which copies have already been made will be erroneously subjected to the copying operation once again, resulting in extra copies. It is also likely that the documents which should be subjected to the copying operation will be overlooked, resulting in failure to make copies of all documents. If copies to be made bear images on both sides, documents that should be re-set must be determined without an error. If an error is made in this determination, the pages of the images on the copies will be numbered erroneously. The copies having such erroneous page numbering may be useless.